If space is an issue than your options are pretty limited. An adult female bp will eat medium rats and my adult male eats medium rats (don't judge me for that I know the "rules"), which is probably too big of a meal for an adult bull snake? Might I suggest getting another bp or 2 and only heating up 1 rat at a time? That way if one refuses you can offer it to another. Or if they're all seeming hungry heat them all up one.